The invention relates to a screwdriver or screwdriver bit, having an input end, an output end and a shank located between these ends, the output end being profiled in the form of at least three, preferably four, ribs, which ribs start, in the radial direction, from a centre section which lies around the axis of rotation, each have a front part at their end, which front part is at an angle to the axis of rotation, and form front and rear flanks which, in the region adjacent to the front part, run substantially parallel to one another, in which region the front flank lies on a diametral surface with respect to the axis of rotation, the flanks Of adjacent ribs forming a notch which runs in the longitudinal direction and has a notch base which ends by running into the circumferential surface of a shank section.
In such known screwdrivers or screwdriver bits, the ribs are centre-offset, specifically by substantially the dimension of the rib thickness. One of the flanks, specifically the frontal flank which lies on the screwing-in side, lies on a common diametral plane with the corresponding flank of the opposite rib (in the case of cross-ribbing, of course). The associated screw head is adapted to these decentralized rib entries. The adjoining rear flank in the same groove is substantially parallel over the insertion depth, but then merges into a concave rounded section, so that the notch boundary edges meet, on the circumferential wall side, at the foot of the completely planar flank. The rounded section covers a quarter-circle. This leads to considerable volumes of material being removed in the region of the base of the output end, resulting in a certain tendency towards weakness.
It is an object of the invention to provide a screwdriver or screwdriver bit of the type in question which is more stable and more advantageous in terms of its screwing performance.
This object is firstly and substantially achieved in the case of a screwdriver or screwdriver bit of this type, it being provided that the two flanks, starting from the front region of each rib, are curved away from one another in the axial direction. This results in a distribution of material in the ribs which is better able to withstand the loads. It is furthermore proposed that the notch boundary edge which faces the front flank, in the further course of the continuously curved flank section, is curved over a smaller circumferential angle than the notch boundary edge of the rear flank. This provides stable rib feet; these feet are rooted in the larger accumulation of material in the transition region with the shaft. This involves both flanks of the rib, since they are curved away from one another in the circumferential direction. By having the curvature of the front flank cover a small circumferential angle, it is possible to produce an even greater steepness, whereas the curvature of the rear flank of the rib, which curvature extends over a correspondingly greater circumferential angle, xe2x80x9creinforces the backxe2x80x9d, as a result of the greater accumulation of material which is formed in that region, in such a manner that it is able to withstand loads. Furthermore, curving both flanks results in an advantageous clamping action between the cross profile, i.e. output end of the screwdriver or screwdriver bit, and the cross slot of the associated screw. This screw is held in place virtually automatically, irrespective of the position.
Moreover, the correspondingly securely gripping insertion method results in high service lives, the application of a high torque and, above all, in the formation of reduced ejecting forces. In addition, it is advantageous, in the case of a screwdriver or screwdriver bit, having an input end, an output end and a shank located between these ends, the output end being profiled in the form of at least three, preferably four, ribs, which ribs start, in the radial direction, from a centre section which lies around the axis of rotation, each have a front part at their end, which front part is at an angle to the axis of rotation, and form front and rear flanks which, in the region adjacent to the front part, run substantially parallel to one another, in which region the front flank lies on a diametral surface with respect to the axis of rotation, the flanks of adjacent ribs forming a notch which runs in the longitudinal direction and has a notch base which ends by running into the circumferential surface of a shank section, if the two flanks in the front part region of each rib are curved away from one another in the circumferential direction, the notch boundary edge which faces the front flank, in the further course of the continuously curved flanks, being curved over a smaller circumferential angle than the boundary notch edge of the rear flank. Furthermore, it is proposed for the front flank to have an additional curvature about the longitudinal direction, with a projecting radially outer section of the front region of the flank. Such a configuration is even in fact of independent importance. It results from a twisting of the ribs which proceeds in the working direction and can be produced in a very wide variety of ways. This also results in flanks which are undercut in the radially inward direction in the front region. The result is an engagement point which lies well on the outside in the radial direction, precisely for screwing in screws, and is therefore particularly advantageous for leverage. Equally, it is advantageous if, in addition, the rear flank has an additional curvature about the longitudinal direction with a correspondingly dropping radially outer section of the front region. Overall, this results in a rib which fits diagonally into the corresponding slot section of the cross slot, assisting with the clamping action explained above. In addition, it is advantageous, in the case of a screwdriver or screwdriver bit, having an input end, an output end and a shank located between these ends, the output end being profiled in the form of at least three, preferably four, ribs, which ribs start, in the radial direction, from a centre section which lies around the axis of rotation, each have a front part at their end, which front part is at an angle to the axis of rotation, and form front and rear flanks which, in the region adjacent to the front part, run substantially parallel to one another, in which region the front flank lies on a diametral surface with respect to the axis of rotation, the flanks of adjacent ribs forming a notch which runs in the longitudinal direction and has a notch base which ends by running into the circumferential surface of a shank section, if the two flanks, in the front region of each rib, starting from a parallel flank section which enters into the insertion profile (cross slot) of the screw head, are curved away from one another in the axial direction, the start of the curvature lying in the region of the opening of the insertion profile. This results in an improved centring fit between screwdriver or screwdriver bit and screw head. To achieve a conical torque set tool, the further measure of having the notch base of each notch, in the front region, inclined at an acute angle to the axis of rotation has proven advantageous. This has a centring action and assists with the clamping action referred to above. Furthermore, it is proposed for the front part of the flanks to form sections of an imaginary frustoconical surface. Furthermore, the invention proposes for the imaginary extension of the axial projection of each notch base to pass the axis of rotation at a distance therefrom. The distance approximately corresponds to the dimension of the smaller circumferential angle of the more steeply curved flank. In addition, it is proposed that the notch base ends with notch boundaries which meet at an acute angle, in which case it is advantageous for the notch boundaries to meet approximately at an angle of about 40xc2x0. Moreover, an advantageous further embodiment of the screwdriver or screwdriver bit of the type in question consists in the distance between point and beginning of curvature being less than the insertion depth of the screw head into the insertion profile. This ensures an advantageous edge contact between tool and attachment element, i.e. screw. In this case, it is advantageous for the width of the rib at the level of the profile depth of the screw head insertion profile to be greater than the width of the opening of the insertion profile. Finally, the invention proposes for the curved surfaces which adjoin the parallel flank section to be twisted. This again results in the abovementioned clamping action between the cross profile, i.e. output end of the screwdriver or screwdriver bit, and the cross slot of the associated screw. Finally, it has proven advantageous for the curved surfaces on the front and rear sides to be unevenly twisted in the same direction, in order to achieve a twisting of the ribs which is more intense at the periphery. The screw profile according to the invention is used in aerospatial engineering, where it is customary for screws to be used only once. The profile according to the invention is particularly suitable for unscrewing the screws, since the flanks of the ribs are not planar, but rather are inherently curved surfaces. The novel geometry is advantageous in particular on the flank which becomes active when unscrewing and does not run through the centre of rotation of the tool. The notch boundary associated with this flank is slightly set back from the groove base, with respect to a parallel plane through the rear flank with respect to the associated rib. The high torque which is required for unscrewing at the start of the screwing movement can be transmitted by the optimum surface-to-surface contact which the geometry produces when torque is applied. At the same time, the profile according to the invention allows the screw to be tightened at least as well as in the prior art, with the maximum torque being produced at the end of the screwing